Cryogenic liquids, for example, liquid nitrogen, oxygen and argon are employed in a number of environments and have a number of industrial and commercial applications in which the user demands high purity which necessitates accurate information as to the analytical content of trace or low level amounts of contaminating gases. Analysis is carried out on a gaseous sample of the cryogenic liquid which typically involves the use of a flash vaporizer.
A particular difficulty arises in obtaining a gas sample which has the same molar concentration of trace contaminants as the cryogenic liquid being sampled.
Thus, for example, liquid nitrogen may typically contain trace amounts of one or more of helium, hydrogen, neon, argon, oxygen, methane, carbon monoxide, carbon dioxide and water. When the temperature of the liquid nitrogen is raised, vaporization or evaporation of the nitrogen and the different contaminating gases takes place at different temperatures and thus at different points in time.
Thus any hydrogen, helium and neon tends to vaporize before the nitrogen and any argon, oxygen, methane, carbon monoxide, carbon dioxide and water tends to vaporize after the nitrogen. In this way fractionation of the sample occurs and the analytical composition of the gas sample continuously obtained varies continuously and does not accurately represent the analytical composition of the cryogenic liquid.
Available samplers do not fully address the problem of fractionation of the cryogenic liquid during volatilization whereby the gas sample is not a true sample of the liquid. In many cases the resulting discrepancies are not serious, however, many users are demanding liquids of ever greater purity so that it becomes increasingly necessary to be able to detect low level contaminants.
Therefore, a need exists in the industry for a cryogenic liquid sampler that satisfies these requirements.